Blue-cone Monochromacy (BCM) is a rare X-lined recessive disorder characterized by poor color discrimination, poor visual acuity ranging from 20/50 to 20/300, and some photophobia. BCM can be caused by a mutation on the q28 region of the X chromosome. Mutations in this region can inactivate red- and green- pigment genes, but in some cases of BCM residual red- and green- pigment gene function is detectable. Nathans et. al. (1993) conducted genetic experiments that classified the cause of BCM into two genetic categories that produce any one of twelve different genotypes. We conducted a study that compared the phenotypic differences between two males with distinctly different genetic mutations both causing BCM. A number of standard color vision tests as well as other psychophysical tests were used to determine the perceptual differences between these subjects. Results indicate that subjects have different degrees of color perception and discrimination. Further, results indicate that both subjects exhibit residual red- and green-pigment cone function. A discussion of possible sources of these differences is included.